Until recently there has persisted a fundamental dichotomy between two main types of telecommunication networks. The first type of telecommunication network, the telephone network, switches and transports predominantly voice, facsimile, and modulation-demodulation system (modem) traffic. The public switched telephone network (PSTN) is an example of this type of network. Telephone networks are also deployed privately within organizations such as corporations, banks, campuses, and government offices. The second type of telecommunication network, the data network, switches or routes and transports data and video between computers. The Internet is an example of a public data network; data networks may be privately deployed.
Telephone networks were developed and deployed earlier, followed by data networks. Telephone network infrastructures are ubiquitous, however, and as a result data networks typically are built, to a limited extent, using some components of telephone networks. For example, the end user access link to a data network in some cases is implemented with a dial-up telephone line. The dial-up telephone line thus connects the end user computer equipment to the data network access gateway. Also, high speed digital trunks interconnecting remote switches and routers of a data network are often leased from telephone long-haul carriers.
Nonetheless, telephone and data network infrastructures were typically deployed together with limited sharing of resources, especially with regards to the core components of the networks—the switches and routers that steer the payloads throughout the networks. Furthermore, multiservice network switches are used to provide a data path, or interface, between multiple networks, each of which may operate using a different type of data or according to a different networking standard protocol. Examples of the networking protocols supported by these multiservice switches include, but are not limited to, frame relay, voice, circuit emulation, T1 channelized, E1 channelized, and Asynchronous Transfer Mode (ATM). The cost of this redundancy coupled with advances in data network technology has led, where possible, to integrated network traffic comprising voice, data, facsimile, and modem information over a unified data network. As such, a network should now be able to accept, service, integrate, and deliver multiple types of data over its access links on a random, dynamic basis using a minimum set of hardware on a single platform. This is typically accomplished using network routers, or concentrators, that provide for dynamic allocation of network resources among the received channels of information on an as-needed basis, wherein the cost, size, and complexity of the router is reduced by minimizing the duplication of resources among router channels.
One type of network technology, ATM, is a connection based technology designed to provide flexible use of network bandwidth in order to support users having diverse service requirements. The functionality provided by a concentrator in an ATM network comprises supporting the Quality of Service (QoS) for each virtual circuit (VC), or connection, supported by the router. The QoS is a set of parameters and measurement procedures defined to quantify loss, errors, delay, and delay variation. The QoS is established when the VCs are established, and the QoS parameters include loss rate, acceptable delay, and peak and average data rates.
A network determines, when a connection request is made, whether sufficient resources exist to allow the connection to be established with the requested parameters, while not impacting the QoS of established connections. If sufficient resources do not exist to support the requested QoS, the connection request is rejected. If sufficient resources do exist to support the requested QoS, a connection is established, and the network ensures that each transmitting station meets the QoS for each VC of that station. Traffic shaping is a procedure used at the transmitting end station and intermediate stations to ensure that the QoS is supported. Traffic shaping parameters typically comprise sustained cell rate (SCR), peak cell rate (PCR), and maximum burst cell count (MBC).
Traffic shaping ensures support of the QoS for established connections by ensuring that the transmission rate for any given VC does not exceed the peak or average data rate allowed for that VC. Specifically, traffic shaping functionality allows an ATM device to control an outgoing cell stream such that the SCR does not exceed a prescribed SCR at any given time, the PCR does not exceed a prescribed PCR at any given time, and the MBC does not exceed a prescribed MBC at any given time. Typical traffic shaping mechanisms require the use of counters, timers, and control logic for each one of the potential VCs of a network station. In particular, at least one timer is used to control the SCR and PCR of a cell transmission. The problem with the typical mechanisms, however, is that, as the number of VCs of a typical network station is large, and as the router must simultaneously support QoS standards for this large number of VCs, the chip silicon area and die size required for the associated counters and timers is significant. Furthermore, and even more problematic, is that in low cost, low speed networks, for example ATM over T1, the additional timer interrupts cause an excessive processor load.